Physics · Ch 13 — Electromagnetic Waves and Communication System
Electromagnetic Spectrum
Electromagnetic Spectrum
The electromagnetic spectrum is the orderly, sequential arrangement of all EM waves according to their wavelength (equivalently, their frequency, since fixes one once the other is known) into distinct named groups, each of which has its own characteristic properties, sources and uses. Table 13.1 tabulates seven such groups -- gamma rays, X-rays, ultraviolet, visible light, infrared, microwaves, and radio waves -- giving the approximate wavelength range, frequency range, and typical generation mechanism for each. The following subsections describe these seven bands one by one, working through the spectrum in order of decreasing wavelength (equivalently, increasing frequency and increasing photon energy), from radio waves at the low-energy end to gamma rays at the high-energy end. …
What this figure shows. A horizontal strip diagram spanning the full electromagnetic spectrum, with the seven named bands -- radio waves, microwaves, infrared, visible light, ultraviolet, X-rays and gamma rays -- arranged in order along the strip, ordered from the longest wavelength / lowest frequency band (radio waves) at one end to the shortest wavelength / highest frequency band (gamma rays) at the other. The narrow visible-light band is highlighted with its constituent spectral colours (violet through red). Approximate wavelength and/or frequency scale markings run alongside the bands to indicate their relative position and extent, summarising visually the same seven-category ordering and numeric ranges tabulated in the accomp …
Name | Wavelength range in m | Frequency range in Hz | Generated By
Gamma rays | 6x10^-13 to 1x10^-10 | 5x10^20 to 3x10^18 | a) Transitions of nuclear energy levels; b) Radioactive substances
X-rays | 1x10^-11 to 3x10^-8 | 3x10^19 to 1x10^16 | a) Bombardment of high energy electrons (keV) on a high atomic number target (Cu, Mg, Co); b) Energy level transitions of innermost orbital electrons
Ultraviolet (UV waves) | 3x10^-8 to 4x10^-7 | 1x10^16 to 8x10^14 | Rearrangement of orbital electrons of atom between energy levels, as in a high voltage gas discharge tube, the Sun and mercury vapour lamp
Visible light | 4x10^-7 to 8x10^-7 | 8x10^14 to 4x10^14 | Rearrangement of outer orbital electrons in atoms and molecules, e.g. gas discharge tube
Infrared (IR) radiations | 8x10^-7 to 3x10^-4 | 4x10^14 to 1x10^12 | Hot objects …